For example, the inkjet head of an inkjet printer generally comprises a plurality of nozzles for ejecting ink droplets therefrom and an ink supply passage communicating with the nozzles.
Recently, it has become necessary to more precisely and more minutely process inkjet heads to permit ultrafine characters to be printed. For this purpose, there have been proposed many methods of forming micropore nozzles by applying anisotropic-etching to a silicon substrate.
It is preferable to use a nozzle having such a cross-sectional shape that a thin nozzle hole portion is formed on the front end side thereof and a nozzle hole portion expanding in a conical shape or a pyramidal shape is formed at the rear end side thereof in order to improve the ink ejection characteristics of the respective nozzles of an inkjet head. For example, as disclosed in Japanese Unexamined Patent Publication No. 56-135075, when a nozzle is formed in a cylindrical shape at the front end side thereof and the inner periphery of the nozzle is formed in a truncated-quadrangular-prism shape at the rear side thereof, the directions of ink pressures imposed on nozzles from an ink cavity side can be aligned in the axial directions of the nozzles, as compared with a case where cylindrical nozzles are used. Stable ink ejection characteristics can be obtained thereby. That is, since variations in the trajectories of ink droplets can be eliminated, they are prevented from flying in differing directions, whereby variations in the amount of the ink droplets can be suppressed.
As disclosed in Japanese Unexamined Patent Publication No. 56-135075, however, since the truncated-quadrangular-prism-shaped inner periphery of the nozzle on the rear side is formed in a silicon substrate using anisotropic-etching, the inner periphery is formed along the crystal direction of the silicon. Thus, the angle of the inclined rear portion of the nozzle is reduced to obtain an action for aligning the directions of ink pressures imposed on the nozzles from the ink cavity side in the axial directions of the nozzles. That is, it is impossible to decrease the cross-sectional area of the nozzle on the rear side thereof.
In contrast, for example, Japanese Unexamined Patent Publication No. 5-50601, filed by the applicants, discloses a method of manufacturing an electrostatic drive type inkjet head in which a nozzle and an ink supply passage are formed with pinpoint accuracy by applying photolithography and wet-type-crystal-anisotropic-etching to a silicon monocrystalline substrate.
The inkjet head disclosed in the publication employs a structure in which nozzles, reservoirs, ink supply passages such as cavities and the like, and diaphragms are formed on a silicon monocrystalline substrate bonded to a glass electrode substrate, on which electrodes for deflecting the diaphragms by electrostatic force are formed.
The use of this structure allows a manufacturing method to be employed in which after the patterns (nozzles, ink supply passages, electrodes) of respective inkjet heads are formed on the respective substrates, the substrates are bonded to each other and the thus-bonded substrates are cut and separated into the respective inkjet heads (the so-called method of making multiple inkjet heads from a single substrate), whereby the inkjet heads can be manufactured at low cost. Note that an example of the method of making multiple inkjet heads from a single substrate is disclosed in Japanese Unexamined Patent Publication No. 9-300630, filed by the applicants. Specifically, the publication proposes a method of bonding a plurality of cover substrates and a flow passage substrate in a row state so that terminals formed at a lower substrate to supply a signal or power are exposed.
Incidentally, when nozzles are formed on a cover substrate for covering an ink supply passage and the cover substrate itself is used as a nozzle plate, it is preferable for accuracy that after a single nozzle plate is bonded to a flow passage substrate, the combined substrate be separated to respective inkjet heads, as compared with the method disclosed in Japanese Unexamined Patent Publication No. 9-300630.
In this case, a through-hole for exposing terminals formed on the lower substrate must be formed, in addition to the nozzles, on the nozzle plate as the uppermost substrate of these three substrates.
Etching is carried out at a relatively low rate in a process for forming nozzle holes because pinpoint processing accuracy is required in the process. In contrast, etching is carried out at a relatively high rate in a process for forming the through-hole whose accuracy is relatively not as stringent as that for the nozzle holes because a reduction in etching time takes precedence over processing accuracy. As a result, the process for forming the nozzle holes and the process for forming the through-hole, the etching conditions of which are different from each other, have ordinarily been performed independently from each other. That is, after the through-hole is formed by etching, the nozzle holes are etched; or after the nozzle holes are formed by etching, the through-hole etched.
Thus, all the sub-processes relating to the etching process, such as patterning including the formation of a resist film, masking, and the removal of the resist film, rinsing, and the like, must be carried out twice, whereby problems arise in that the manufacturing process is complex and the manufacture is time-consuming.
Problems to be solved by the present invention, which was made in view of the above points, primarily reside in the following two points:                1) to propose a method for forming a nozzle for an ejection device in a monocrystalline silicon substrate, the nozzle having a substantial action for aligning the directions of pressures imposed on nozzles from a cavity side in the axial directions of the nozzles, as compared with the action obtained by a conventional method; and        2) to propose a method for manufacturing an inkjet head capable of forming a nozzle without lowering the processing accuracy thereof, as well as capable of forming a through-hole, which is very large relative to the nozzle, on a monocrystalline silicon substrate simultaneously with the formation of the nozzle, thereby simplifying the manufacturing process and reducing manufacturing time.        